The present invention relates to a method of forming a shaped-body to be sintered, which is suitable for forming from a slurry serving as a sintering material a shaped-body to be sintered, such as a body with a complicated configuration or the like.
Hitherto, various methods have been used to form from ceramic powders shaped-bodies which are to be sintered. A slip casting method is one of them and is widely used as a method of forming shaped-bodies with complicated configurations.
It is known to use a gypsum mold in a slip casting method. However, the use of the gypsum mold has encountered such problems as a difficulty found in releasing a shaped-body with a complicated configuration from the mold used, and a poor durability of such molds. To cope with these problems, the present inventors have previously proposed a method (Japanese Patent Unexamined Publication No. 62-268603) wherein a shielding member, which is impermeable to air and is dissolvable in a solvent for the slurry to be used or a porous shielding member which is permeable to the slurry solvent, is tightly adhered to the forming surface of a pattern member, a frame is disposed on the side of the shielding member that is remote from the pattern member, a substance formed of particles is charged into the frame, the upper surface of the particle-formed substance is sealed and then a negative pressure within the frame is produced to thereby allow the shielding member to be sucked onto the particle-formed substance, the pattern member is separated from the shielding member to thereby prepare one half of a mold having a molding surface, the thus prepared mold part is joined to another half of the mold which has been prepared by the same processes as those described above to thereby define a cavity, a slurry comprising a sintering material and a solvent added thereto is poured into the cavity, and the negative pressure within the frame is released to cause the molding surface to collapse.
The previously proposed method, however, has encountered the following problems In the process of tightly adhering a shielding member which is impermeable to air and dissolvable in a slurry solvent or a porous shielding member which is permeable to the slurry solvent, to the forming surface of the pattern member, the shielding member is subjected to a softening treatment in which it is heated by a burner or the like to enhance the flexibility of the shielding member. If, for instance, a polyvinyl alcohol film is used, the heating of the film causes dehydration reactions and changes in properties, resulting in the production of polyvinyl ether, thereby making part of the film insoluble in the solvent. In such cases, therefore, when the slurry has been poured, the absorption and removal of the slurry solvent by the shielding member may become uneven, causing uneven wall thickness to be obtained and low permeation of the slurry solvent, which in turn may result in the generation of local defects (holes) and, hence, the production of a defective sintered body. Further, the changes in the properties of part of the shielding member cause concentrated stress, leading to partial breakage of the shielding member and, hence, leakage of the slurry. In cases where other types of resins are used, the heating treatment causes chemical reactions and changes in properties, resulting in similar problems.